The present invention relates to a multi-high rolling mill whose sections above and below a rolled material have different numbers of rolls and, more particularly, to a five-high rolling mill, a multi-high rolling mill, a skinpass rolling mill, and a rolling method of the multi-high rolling mill which are suitable for skinpass rolling or rolling of aluminum.
In general, as a rolling mill of a small rolling reduction and a small rolling force, e.g., a skinpass rolling mill, there has conventionally been often employed a four-high rolling mill which includes upper and lower work rolls provided with bending devices and upper and lower backup rolls supporting these work rolls, as disclosed in Japanese Patent Unexamined Publication No. 48-22344.
However, such a four-high rolling mill does not have a sufficient ability in shape control, and insufficiency of this ability is compensated with various work rolls provided with different crowns. That is why a six-high rolling mill which is superior in the shape control ability has been suggested and applied to practical use (see Japanese Patent Examined Publication No. 57-55484). This six-high rolling mill is arranged in such a manner that upper and lower intermediate rolls are disposed between upper and lower work rolls of the same diameter and upper and lower backup rolls of the same diameter, respectively, and that roll bending devices are installed on the upper and lower work rolls and the upper and lower intermediate rolls, both sets of these bending devices being capable of providing a great ability in the shape control. In case of skinpass rolling with a small rolling reduction, this six-high rolling mill causes portions of the side ends of a rolling stock to remain non-rolled so that edge wrinkles are formed on the side ends of the rolling stock, thereby resulting in a problem that formation of such edge wrinkles cannot be adequately prevented.
A conventional multi-high rolling mill whose sections above and below a rolling stock have different numbers of rolls or a conventional five-high rolling mill in particular is disclosed in each of Japanese Patent Examined Publication Nos. 60-48242 and 62-46245. Such a five-high rolling mill includes upper and lower work rolls of different diameters, with the upper work roll being a roll of the smaller diameter, and thus, a large rolling reduction can be obtained from a small rolling force. Further, bending devices are installed on both the intermediate roll and the lower work roll of the larger diameter so as to cause the five-high rolling mill to exhibit its ability in controlling a sheet crown. Hence it is possible to control a simply curved (concaved or convex) crown of the rolling stock in its entire width, decrease the rolling force, and enhance the effect of the benders as a result.
On the contrary, in case of i) a rolling operation with both the rolling reduction and the rolling force having small values, ii) a rolling operation which requires an excellent ability in the sheet surface control enabling composite shape control, and iii) a rolling operation which requires prevention of the edge wrinkles, for example, in case of skinpass rolling, rough-surface dull rolls, that is, work rolls in the above-mentioned five-high rolling mill including the upper and lower work rolls of different diameters are extremely shortened in life, and the rolled material is apt to be unfavorably warped. Besides, if the work rolls have small diameters, another Problem is caused in that a cross buckle or a folding is apt to be generated during the rolling operation.
A five-high rolling mill including an intermediate roll which has the same drum length as the width of the rolled strip sheet, in which upper and lower work rolls of the same diameter are provided with bending devices, is disclosed in each of Japanese Patent Unexamined Publication No. 54-39349 and Japanese Patent Examined Publication No. 53-34789.
In use of such five-high rolling mills, it is necessary to replace the intermediate roll with a new one every time the sheet width of the rolled strip sheet is changed, and the rolling operation must be stopped on each such occasion, so that the productivity of the rolling mill will be lowered to a great extent, and the rolling mill will fail to be practical in use. Especially in case of a skinpass rolling mill installed in a continuous annealing line, since a rolling stock of different widths are continuously supplied thereto, the above-mentioned five-high rolling mill is quite unlikely to be applied to practical use.
Further, five-high rolling mills in which upper and lower work rolls are of the same diameter and these upper and lower work rolls and an intermediate roll of a diameter smaller than that of the work rolls are respectively provided with bending devices is disclosed in Japanese Patent Unexamined Publication No. 56-151103. However, the intermediate roll of such five-high rolling mill which has a small diameter and the same drum length as that of the backup roll and the work roll, is in contact with the backup roll and the work roll over its entire length, and therefore, the control characteristic of the intermediate roll becomes similar to that of the upper work roll, thereby resulting in a problem that it is basically impossible to accomplish either the composite shape control or the control for prevention of the edge wrinkles.